Problems with Zaid's compilation of Quran

From multiple hadiths of bukhari, we came to know that loss of Quran memorizers prompted Abu Bakr and Umar to assign Zaid to collect the Quran in one book which Muhammad didn't do in his lifetime. Now there are some questions related to the Two witnesses criteria:

• Why was this criteria adopted? Why not 3 witnesses or 4? Who came to the conclusion that 2 witnesses are enough?

• What was expected from these witnesses to testify on isn't clear. Muslim apologist like this argue that, simply to have listened from muhammad wasn't enough. They must had to testify on verses which were written in front of muhammad.

• What about the literary eloquence of Quran? Why eloquence was never a criteria for inclusion or exclusion of a verse for Zaid and his Quran collection team? Somehow it didn't seem a valid criteria to them.

Zaid compiled the Quran based on the criteria of two witnesses. Any verses written anywhere which didn't have two witnesses was not considered part of Quran & was discarded. If this is how the process underwent then one might wonder whether there were actual verses excluded from Muhammad's Quran simply because lack of 2 witnesses! Consider this: In the Itqan, while discussing of the number of witnesses, al-Suyuti quotes from Ibn Ashta's Kitab al-Masahif that,

The people would come to Zaid ibn Thabit and he would only write a verse from two upright witnesses. Even though the end of Surat al-Bara'a was not found except with Khuzaima ibn Thabit, he said: Write it, for God's messenger, peace and blessings be upon him, made his testimony as the testimony of two men. So it was written, even though Umar brought the verse of stoning and it was not written because he was alone (Ibn Ashta in al-Suyuti vol. 1,58).

Khuzaima who testified for the written verse, we know from this hadith that his testimony had the value that of two witnesses. In the same way, though Umar and others knew Muhammad recited the verse of stoning, this verse wasn't included in the Quran because there was no 2nd witness who could have testified for it with Umar.

Umar was outspoken of this verse. Early islamic scholars tried to reconcile this by claiming that, the recitation of this verse is abrogated while ruling still applies! To me it appears as a convenient excuse. More on this verse and others here and here.

Ibn Abi Dawud in Kitab al-Masahif, p. 23 wrote,

Many (of the passages) of the Qur'an that were sent down were known by those who died on the day of Yamama....but they were not known (by those who) survived them, nor were they written down, nor had Abu Bakr, Umar or Uthman (by that time) collected the Qur'an, nor were they found with even one (person) after them.

According to one report by the son of the second caliph Umar given by Suyuti in his al-Itqan part 3, page 72, the present text of the Quran is incomplete since much of it has disappeared:

Abdullah b. Umar reportedly said, 'Let none of you say, "I have got the whole of the Qur'an." How does he know what all of it is? Much of the Quran has lost [arabic: Dhahab also used in this hadith]. Let him say instead, " I have got what has survived."

Read detailed explanation here and see why Gibril's response is incorrect.